Deposition of thin films on a substrate surface is an important process in a variety of industries including semiconductor processing, diffusion barrier coatings and dielectrics for magnetic read/write heads. In the semiconductor industry, in particular, miniaturization requires atomic level control of thin film deposition to produce conformal coatings on high aspect structures. One method for deposition of thin films with atomic layer control and conformal deposition is atomic layer deposition (ALD), which employs sequential, surface reactions to form layers of precise thickness controlled at the Angstrom or monolayer level. Most ALD processes are based on binary reaction sequences which deposit a binary compound film. Each of the two surface reactions occurs sequentially, and because they are self-limiting, a thin film can be deposited with atomic level control. Because the surface reactions are sequential, the two gas phase reactants are not in contact, and possible gas phase reactions that may form and deposit particles are limited. The self-limiting nature of the surface reactions also allows the reaction to be driven to completion during every reaction cycle, resulting in films that are continuous and pinhole-free.
ALD has been used to deposit metals and metal compounds on substrate surfaces. Al2O3 deposition is an example of a typical ALD process illustrating the sequential and self-limiting reactions characteristic of ALD. Al2O3 ALD conventionally uses trimethylaluminum (TMA, often referred to as reaction “A” or the “A” precursor) and H2O (often referred to as the “B” reaction or the “B” precursor). In step A of the binary reaction, hydroxyl surface species react with vapor phase TMA to produce surface-bound AlOAl(CH3)2 and CH4 in the gas phase. This reaction is self-limited by the number of reactive sites on the surface. In step B of the binary reaction, AlCH3 of the surface-bound compound reacts with vapor phase H2O to produce AlOH bound to the surface and CH4 in the gas phase. This reaction is self-limited by the finite number of available reactive sites on surface-bound AlOAl(CH3)2. Subsequent cycles of A and B, purging gas phase reaction products and unreacted vapor phase precursors between reactions and between reaction cycles, produces Al2O3 growth in an essentially linear fashion to obtain the desired film thickness.
While perfectly saturated monolayers are often desired, this goal is very difficult to achieve in practice. The typical approach to further ALD development has been to determine whether or not currently available chemistries are suitable for ALD. Prior art processes for ALD have been most effective for deposition of metal oxide and metal nitride films. Although a few processes have been developed that are effective for deposition of elemental ruthenium and other late transition metals, there is a need for new elemental metal deposition chemistries that are commercially viable.
Additionally, during the manufacture of integrated circuits, there is often a need to deposit metal films onto other metal surfaces, but avoid depositing metal onto exposed dielectric regions. For example, there may be copper on the bottom of a via that has low-k dielectric sidewalls. In order to complete fabrication of the integrated circuits, it is necessary to deposit a metal over the existing copper metal areas, but avoid the dielectric areas. Thus, there is a need for a method of deposition that is selective for metals, and will avoid such deposition onto the exposed dielectric regions.
The present invention addresses these problems by providing novel chemistries which are specifically designed and optimized to take advantage of the atomic layer deposition process. In fact, before the present invention, there were no known commercially acceptable atomic layer deposition precursors that are capable of selectively depositing cobalt and/or manganese onto metal surfaces.